The non-native barnacle species Austrominius modestus was first recorded in Ireland, close to Lough Hyne
marine nature reserve in 1957. This species was not recorded inside the Lough until 1980, but by 2001
was the dominant intertidal barnacle within the reserve. It has been suggested that increases in the
abundance of this species at other locations in Europe may be linked to increasing sea surface temperatures,
and that A. modestus is an “ecological sleeper”. Despite an overall trend for increasing sea
surface temperatures, this long term warming is punctuated by extreme events such as severely cold
winters. A. modestus is warm water adapted, and has been recorded to decrease in abundance following
cold winters. The winters of 2009/2010 and 2010/2011 were amongst the coldest recorded in Ireland in
past decades. In the present study, higher levels of mortality were recorded for A. modestus than native
barnacle species in Lough Hyne following these cold winters. Additionally, this species was recorded at
lower abundances at the majority of sites surveyed in Lough Hyne in 2011 compared with 2009. Despite
this, A. modestus remains the dominant barnacle species in the Lough and monitoring the recruitment of
intertidal barnacles within Lough Hyne during 2014e2015 revealed that A. modestus was the most
abundant recruit at study sites, both in removal plots and in the pre-existing community. The year-round
breeding of A. modestus in addition to the closed nature of the Lough promotes A. modestus within the
reserve. Despite this, native barnacle species continue to persist in Lough Hyne, though generally at low
abundances, with the exception of exposed locations such as the Rapids and Bullock Island where natives
outnumber A. modestus. The future intertidal barnacle community within the Lough is likely to be
dominated by A. modestus with Chthamalus montagui and C. stellatus being abundant at sites which are
not suitable for A. modestus. While the consequences of this are unknown, it is possible that the presence
of A. modestus may alter trophic interactions and energy flow within the reserve.